The HTC Radar 4G just arrived at T-Mobile this week, but if you were expecting to have to wait a little before any really good deals on the phone came around, we’ve got a pleasant surprise for you. If you’ve got an old phone in working condition that’s just been gathering dust, T-Mobile’s got a trade-in promotion going that can net you the Radar for pretty much nothing on-contract.

While this may not be quite free, since you’ve got to factor in the value of your old phone, we’re betting more than a few of you have old dumbphones lying around in a drawer that you never plan on using again. Simply go to T-Mobile’s trade-in site, enter the code “MSMango”, and it will get you started. No matter what phone you’re trading-in, you’re guaranteed at least $100, making the Radar free; have a better phone, and you could see even more, effectively making money off the deal.

Keep in mind, you won’t be seeing the savings straight away, as the phone’s normal price includes a $50 mail-in rebate card, and this trade-in deal involves a separate mail-in rebate. An instant rebate would be nice, but considering you’re getting a brand-new phone for practically nothing, we can can live with the inconvenience.